Blends of two or more polymers have often been made in attempts to combine desirable properties of the individual polymers into the blend, to seek unique properties in the blend, or to produce less costly polymer products by including less expensive polymers. For example, many attempts have been made to blend polyamide resins such as nylon-6 and nylon-66, and polyolefin materials. Polyamide resins have excellent chemical and abrasion resistance, good oxygen barrier properties, good electrical properties, and superior mechanical strength, but are very sensitive to moisture and are difficult to process due to their high melting temperature. Polypropylene is a low cost, low density, semi-crystalline polymer with excellent moisture resistance that is capable of being recycled and is easy to process.
However, it is difficult to obtain a good dispersion of a polar engineering thermoplastic resin and a non-polar polyolefin resin. It is known that the addition of a graft or block copolymer of similar chemical structure to the blend components can improve the quality of the dispersion. These copolymer additives, generally referred to as compatibilizers, are often added to the blend as a third component.
Graft copolymers of alpha, beta-unsaturated carboxylic acids and anhydrides on a polypropylene backbone have often been used as compatibilizers for polypropylene/polyamide blends. Carboxylic acids and copolymers thereof, or maleic anhydride functionalized styrene/ethylene-butylene/styrene copolymers, have also been used with some success. For example, U.S. Pat. No. 5,290,856 discloses blends of polyamide, polyphenylene ether, or polyester resins with polyolefin graft copolymers such as polypropylene grafted with a styrenic polymer and a glycidyl moiety. U.S. Pat. No. 6,319,976 discloses a blend of a polyamide resin, a broad molecular weight distribution propylene polymer material, and a graft copolymer comprising a backbone of a propylene polymer material having graft polymerized thereto monomers selected from (i) at least one vinyl aromatic compound and an unsaturated carboxylic acid and (ii) at least one vinyl aromatic compound and an anhydride of an unsaturated carboxylic acid.
Ionomers of graft copolymers comprising a backbone of a polyolefin having graft polymerized thereto polymerized monomers containing acid or anhydride groups have also been used to improve adhesion between polyolefins and polar polymers such as polyamides and other engineering thermoplastics. U.S. Pat. No. 5,137,975 discloses a method for preparing a compatibilizer by contacting a molten polypropylene grafted with an unsaturated acid or anhydride with an aqueous solution of a hydroxide, carbonate or bicarbonate of an alkali metal to form an ionomer. U.S. Pat. No. 4,219,628 discloses a polyester composition containing an ethylene-propylene copolymer rubber, and an ionomer of poly(ethylene-co-acrylic acid) in which about 50% of the acrylic acid is converted to a metal salt. U.S. Pat. No. 4,885,340 describes a high impact polyamide composition comprising at least one polyamide, at least one ethylene ionomer resin, and at least one oxide or carbonate compound. U.S. Pat. No. 5,013,789 describes a process for producing a thermoplastic resin composition by adding an unsaturated carboxylic acid or a derivative thereof to a first crystalline polypropylene, a second crystalline polypropylene, and a polyamide; mixing the component with at least one hydroxide, carbonate or oxide of a metal of Groups I, II or m of the Periodic Table, and subsequently melt-mixing the mixture. U.S. Pat. No. 5,534,335 discloses a non-woven fabric made from fibers comprising at least two thermoplastic polymers, i.e., a polyamide and polypropylene, and a compatibilizer such as a zinc ionomer of an ethylene/methacrylic acid copolymer or polypropylene modified with maleic anhydride.
However, there is still a need for compatibilizers for blends of polyolefins and engineering thermoplastics that provide a good balance of properties including strength, stiffness, good gloss, and scratch and mar resistance and which when converted into film also exhibit good barrier properties.